Conventional fluid actuated torque transmissions, for example, clutches and brakes, have a plurality of axially aligned friction plates which are alternately splined with an inner member and an outer member. In the case of a clutch, one member is connected with a rotatable shaft and the other member is connected with a gear element. In the case of a brake, one member is connected with a stationary housing and the other member is connected with a shaft or gear.
The friction plates are forced into frictional engagement by pressure on a fluid operated axially movable piston. The piston has an apply surface that directly engages one of the plates which is axially aligned therewith. However, the piston has a larger annular area than the friction plates, resulting in the center of pressure being radially offset from the apply surface. This establishes an overturning moment on the piston. The piston is urged to the disengaged position by a plurality of return springs when the pressure is reduced.
The piston and friction plates are stacked in series in an axial direction. This requires that the torque transmitter be provided with an overall axial dimension to the accommodate the plates, piston, axial movement of the piston and the housing in which the piston is selectively disposed. Also, the piston establishes sufficient structure and bearing surfaces to accommodate the overturning moment. This axial positioning within the transmission utilizes valuable space under the hood of the modern passenger vehicle. The piston structure can impose weight and cost factors which increase the overall cost of the transmission.